Method for recovering rhodium from reaction products of oxosynthesis

ABSTRACT

The invention relates to a method for separating and recovering rhodium from reaction products of oxosynthesis, especially reaction products containing cobalt. The invention also relates to the reuse of rhodium as a catalyst for hydroformulation and to a catalyst for hydroformulation itself. The inventive method is characterized by the following: extraction of the organic solution with an aqueous phosphate solution or a phosphate solution, water washing, oxidative treatment of the organic phase, and extraction of the organic phase with an aqueous water-soluble arylphosphine solution.

[0001] The present invention relates to an improved process for removingand recovering rhodium from oxo process reaction products.

[0002] The preparation of aldehydes and alcohols by addition of carbonmonoxide and hydrogen to olefinic double bonds (hydroformylation) iswell known. The reaction is catalyzed by metals or compounds thereof ofthe 8^(th) transition group of the Periodic Table which form carbonyl orhydridocarbonyls under the reaction conditions. While cobalt and cobaltcompounds used to be used as catalysts, rhodium catalysts are todayfinding use to an increasing extent, even though rhodium is severaltimes more expensive than cobalt. Rhodium is used alone or incombination with complexing agents, for example organic phosphines.While the oxo process requires reaction pressures of from 25 to 30 MPausing rhodium as catalyst, pressures of from 1 to 5 MPa suffice whenrhodium complexes are used.

[0003] In many cases, rhodium catalysts have distinct advantages. Theyhave higher activity and selectivity and additionally facilitateuncomplicated operation of the production plants, in particular relatingto conduct of the synthesis and the excavation of the products from thereactor. Finally, the classic oxo process based on cobalt catalysts maybe converted in many cases to rhodium catalysts using the availableapparatus parts with only minimal capital expenditure.

[0004] Despite the advantages mentioned of the rhodium-catalyzed oxoprocess, the classic cobalt process continues to be operated in existingold plants, in particular when conversion of the process to the rhodiummethod under the given economic conditions does not appear necessary.

[0005] Particular significance attaches to the recovery of rhodiumwhich, after the reaction has ended, is present as the carbonyl compounddissolved in the hydroformylation product. The work up comprisesdepressurizing the crude oxo product in more than one stage by reducingthe synthesis gas pressure from about 25 to 30 MPa initially to from 1.5to 2.5 MPa. This releases synthesis gas dissolved in the crude product.The mixture can then be depressurized to atmospheric pressure. Beforepurification or further processing of the reaction product, bydistillation, the dissolved rhodium compounds have to be removed. It hasto be taken into account here that only a few ppm of the noble metal arepresent homogeneously dissolved in the crude product. Also, in thecourse of the depressurization procedure, rhodium can be converted to ametallic form or form multinuclear carbonyl compounds which separatefrom the liquid organic phase as solids.

[0006] In the process known from EP-A-147824, rhodium is removed andrecovered by extracting it from the crude oxo product by means ofcomplexing reagents.

[0007] The crude oxo product is the oxo process reaction mixtureobtained after depressurizing and possible cooling.

[0008] In the known process, the complexing agents used are sulfonatedor carboxylated organic phosphines, preferably sulfonatedarylphosphines. The sulfonated or carboxylated organic phosphines formwater-soluble complexes with rhodium. Accordingly, the rhodium may beextracted from the crude organic product using an aqueous solution ofthe substituted phosphine.

[0009] This transfers the rhodium to the aqueous phase which can beremoved by simple decanting from the organic product mixture.Circulation of the complexing agent solution provides high rhodiumconcentrations in the aqueous phase.

[0010] According to EP-A-156253, the process disclosed by EP-A-0147824is improved by adding a solubilizer to the aqueous solution of thecomplexing agent. Its effect is in particular to alter the physicalproperties of the surface area between the two liquid phases and therebyto accelerate the transfer of the aqueous extractants into the productphase and that of the rhodium from the product phase into the aqueousphase. However, the effectiveness of the process described depends onthe quantity of solubilizer added. Its quantity cannot be increasedwithout limitation because the materials added unnecessarily burden theaqueous solution of the extractant and compromise its stability.

[0011] In the process disclosed by EP-B1-0 183 200, the depressurizedcrude oxo product is likewise extracted using an aqueous solution of acomplexing agent. However, this process does not operate with theaddition of a solubilizer, but instead employs sulfonated arylphosphineshaving quaternary ammonium counter ions, for example thebenzyltrimethylammonium cation, as water-soluble complexing agents.

[0012] The prior art processes employ a catalyst solution which resultsfrom hydroformylation reactions with rhodium catalysis.

[0013] However, problems occur where a hydroformylation plant initiallyoperated under cobalt catalysis is to be converted to rhodium catalysis.

[0014] For instance, EP-B1-0 111 257 concerns a hydroformylation processwhich comprises reacting the off gas from a first hydroformylation step(which reacts olefin with carbon monoxide and hydrogen in the presenceof a catalyst solution comprising an aqueous rhodium complex at lowpressure) in a second step by the classical oxo process at high pressureand in the presence of cobalt catalysts.

[0015] The conversion of this process to the complete rhodium method,i.e. also carrying out the/second step under rhodium catalysis, is thesubject matter of EP-A1-0 805 138.

[0016] The organic phase resulting from conversion to the rhodium methodaccordingly comprises both rhodium and cobalt as catalytically activemetal.

[0017] Since rhodium is a precious metal, there is accordingly greatinterest in its removal, recovery and reuse as active catalyst metalfrom the cobalt-containing catalyst solution for economic reasons. It isof decisive importance that the rhodium occurs virtually completely in aform which allows reuse as a catalyst component. In order to obtainhighly optimal activity and selectivity for the recovered catalyst,virtually complete removal of the cobalt from the rhodium is sought. Itshould likewise be possible to recover rhodium virtually completelywhile at the same time retaining the activity and selectivity of thecatalyst solution after complete removal of the cobalt from thehydroformylation process or from the oxo process reaction products whichwere hitherto obtained by exclusive rhodium catalysis.

[0018] It is accordingly an object of the present invention to provide aprocess by which rhodium may be virtually completely recovered from anorganic catalyst solution in a simple manner. The catalyst solution mayadditionally comprise cobalt-containing compounds as impurities. At thesame time, it shall be ensured that rhodium is obtained in a formsuitable for reuse as catalyst. The rhodium compounds obtained shall besuitable for reuse both in a homogeneous hydroformylation processcarried out in the organic phase and also in the biphasichydroformylation process in the presence of water disclosed by DE-C-2627 354.

[0019] This object is achieved by a process for recovering rhodium fromorganic solutions comprising rhodium complexes with or without cobaltcomplexes and with or without complexing ligands, which comprises

[0020] extracting the organic phase with an aqueous solution of aphosphate of the formula (O)P(OR¹)(OR²)(OR³), where R¹, R² and R³ areidentical or different and are hydrogen, a straight-chain or branchedalkyl radical having 1-10 carbon atoms or a substituted or unsubstitutedaryl radical having 6-10 carbon atoms, and the aryl radical issubstituted by straight-chain or branched alkyl radicals having 1-4carbon atoms, or with a phosphonate of the formula R⁴P(O)(OR⁵)(OR⁶),where R⁴, R⁵ and R⁶ are identical or different and are hydrogen, astraight-chain or branched alkyl radical having 1-10 carbon atoms or asubstituted or unsubstituted aryl radical having 6-10 carbon atoms, andthe aryl radical is substituted by straight-chain or branched alkylradicals having 1-4 carbon atoms;

[0021] washing the organic phase with water at a pH of from 0 to 8;

[0022] treating the organic phase after phase separation with anoxidizing agent at a temperature of from 0 to 100° C.;

[0023] treating the organic phase with an aqueous solution of awater-soluble arylphosphine at elevated temperature and elevatedpressure;

[0024] and removing the rhodium-containing aqueous solution from theorganic phase by phase separation.

[0025] The procedure according to the invention is generally suited torecovering rhodium from an organic phase. An example of such an organicphase is the crude oxo product which is the reaction mixture resultingfrom the hydroformylation reaction after depressurization and optionalcooling, or the distillation residue of the crude oxo product afterremoving the aldehyde. Additionally, the organic phase may possibly alsocomprise cobalt compounds and/or complexing ligands, which is the casewhen a hydroformylation process hitherto carried out under cobaltcatalysis has been converted to the rhodium method. However, the processaccording to the invention may also be applied to rhodium recovery whenthe cobalt quantity originally present has been discharged in themeantime or the hydroformylation process has always been operated underrhodium catalysis.

[0026] The organic phase introduced into the recovery process comprises,in addition to the desired aldehydes, condensation products thereof andalso alcohols. Complex ligands may also possibly be present, dependingon whether the old cobalt process was carried out in the presence of acomplexing ligand and whether the rhodium process is carried out usingcomplexing ligands. However, it is also possible to add complexingligands to the organic phase resulting from the hydroformylationreaction before further work up to stabilize rhodium complexes. Thecomplex ligands present are customary ligands in hydroformylationprocesses such as alkyl phosphines, alkylarylphosphines orarylphosphines, for example triphenylphosphine. Further componentspresent may include oxides derived from the complexing ligands, forexample triphenylphosphine oxide, which are dissolved in the organicphase.

[0027] The operation explained in the following describe the work up ofa rhodium-containing catalyst solution which additionally comprisescobalt compounds as impurities. It will be appreciated that theprocedure according to the invention can also be applied to thosecatalyst solutions comprising organic rhodium from which the cobalt hasalready been completely removed or which come from a hydroformylationprocess carried out in the organic phase under rhodium catalysis.

[0028] As well as cobalt, rhodium is present at a concentration of from10 to 10 000 ppm, in particular from 100 to 5 000, preferably from 200to 1 000 ppm by weight, based on the total mass of the solution. Thecobalt content is generally from 10 to 5 000 ppm by weight, based on thetotal mass of the solution. In the further course of thehydroformylation process carried out under rhodium catalysis, the cobaltcontent falls owing to the continuous discharge from thehydroformylation process. The organic phase comprises from 1 to 20, inparticular from 1 to 10, preferably from 2 to 6% by weight of complexingligands, based on the total mass of the organic phase. In addition,there are also oxidation products of the complexing ligands, such asphosphine oxides. The concentration is generally from 1 to 10% byweight, based on the total mass of the organic phase. The organiccomponents present include aldehydes, alcohols, aldols, condensationproducts and possibly olefin, if an olefin having at least 4 carbonatoms had been used for the hydroformylation reaction. Their relativequantity ratios depend on whether the crude oxo product or thedistillation residue obtained therefrom is selected for the work upprocess according to the invention.

[0029] With the aid of the process according to the invention, it ispossible to remove rhodium which is generally present in lowconcentration with surprisingly high selectivity and yield from thecobalt present in excess.

[0030] In the process according to the invention, cobalt is firstremoved from the organic phase present.

[0031] To this end, the organic phase is extracted with an aqueoussolution of a phosphate of the formula (O)P(OR¹)(OR²)(OR³). R¹, R² andR³ are identical or different and are hydrogen, a straight-chain orbranched alkyl radical having 1-10 carbon atoms, preferably 1-5 carbonatoms, or a substituted or unsubstituted aryl radical having 6-10 carbonatoms. The aryl radical may be substituted by straight-chain or branchedalkyl radicals having 1-4carbon atoms. Preference is given to using anaqueous phosphoric acid solution or an aqueous solution of trimethylphosphate for extraction.

[0032] Aqueous phosphonate solutions can also be used in the extractstep. Useful phosphonic acids include compounds of the formulaR⁴P(O)(OR⁵)(OR⁶). R⁴, R⁵ and R⁶ are identical or different and arehydrogen, a straight-chain or branched alkyl radical having 1-10 carbonatoms, preferably 1-5 carbon atoms, or a substituted or unsubstitutedaryl radical having 6-10 carbon atoms. If the aryl radical issubstituted, it carries straight-chain or branched alkyl radicals having1-4 carbon atoms. Preference is given to using an aqueous phosphonicacid solution where R⁴ is methyl, ethyl, propyl or butyl or an aqueoussolution of methyl dimethylphosphonate for extraction.

[0033] The concentration of the extractant in the aqueous solution isvariable over a wide range. In general, aqueous solutions are used wherethe concentration of the phosporos-containing extractants is from 1 to95, preferably from 30 to 60% by weight, based on the aqueous extractionsolution.

[0034] When the extraction of cobalt is carried out at atmosphericpressure, operation is effected at a temperature of from 0 to 100° C.,preferably 20 to 40° C. However, it is also possible to treat theorganic phase with aqueous extractants under pressure at temperatures offrom 100 to 200° C., preferably from 120 to 140° C. When operation iseffected at temperatures above 100° C., the pressure is generally from0.5 to 20 MPa.

[0035] In order to achieve sufficient phase separation, the volume ratioof organic phase to aqueous extraction phase ranges from 20:80 to 80:20,preferably from 40:60 to 60:40. The extraction is generally carried outover a duration of from 0.5 to 5 hours, preferably from 1 to 3 hours.

[0036] The extraction step is generally repeated more than once, and theorganic phase is generally extracted from 2 to 4 times in succession.

[0037] To remove remaining quantities of extractant, the treated organicphase is admixed with water at a temperature of from 0 to 100° C.,preferably from 20 to 40° C. The water quantity is generally from about25 to 50% of the volume of the organic phase present. Water washing iscarried out at a pH in the range from 0-8, preferably 4-8. To adjust thewashing water to the desired pH, an aqueous solution of an alkalinesubstance having a concentration of from 3 to 20% by weight is generallyadded to the washing water. Preference is given to using aqueoussolutions of alkali metal hydroxides, alkaline earth metal hydroxides,alkali metal carbonates, alkaline earth metal carbonates, alkali metalhydrogen carbonates or alkaline earth metal hydrogen carbonates, inparticular sodium hydroxide or potassium hydroxide.

[0038] To achieve complete phase separation, it is frequently advisableto add an organic solvent. Useful solvents include aliphatichydrocarbons having from 6 to 12 carbon atoms, aromatic hydrocarbonshaving from 6 to 12 carbon atoms, aldehydes or condensation productsthereof. It is particularly advisable to add exactly the aldehyde whichwas the target product of the oxo process. The quantity of the organicsolvent added corresponds to the quantity of the organic phase treated.

[0039] The extraction to be carried out according to the inventiveprocess with subsequent water washing and pH adjustment leads to areduction of the cobalt content in the organic phase treated of morethan 90%, based on the cobalt quantity originally present.

[0040] The organic phase present after extraction and water washing isthen subjected to an oxidative treatment. The oxidation of the organicphase is carried out at temperatures of from 0 to 100° C., in particularfrom 30 to 60° C. and preferably from 50 to 60° C. Since the organicphase comprises aldehydes which either stem from the oxo process or havebeen added to support phase/separation during water washing, carboxylicacids are formed during the oxidation. The formation of the carboxylicacids and further oxidation products from the organic components isexothermic. In order to avoid an uncontrolled oxidation reaction,countercurrent cooling of the oxidation reactor may be required. In thecourse of the oxidation, not only the complexing ligand present inexcess, but also the rhodium complex itself will be attacked, whichconverts the ligand to a form which is no longer suitable forcomplexation. The phosphine oxides arise from the phosphines generallyused as complexing ligands and the rhodium complex falls apart.

[0041] The oxidizing agent used is pure oxygen or oxygen-containing gasmixtures, in particular air. However, it is also possible to use otheroxidizing agents, such as hydrogen peroxide, hydrogen peroxide-formingcompounds, hypochlorite, chromates or permanganates.

[0042] The oxidation may be carried out either under atmosphericpressure, or else under elevated pressure. Useful pressures are from 0.1to 2.0, in particular from 0.2 to 1 and in particular from 0.3 to 0.7MPa.

[0043] The oxidation time is generally from 0.5 to 24 hours. The exactoxidation time depends on the content of the complexing ligand in theorganic phase and may be determined by simple preliminary experiments.The course of the oxidation reaction is determined by gas chromatographydetermination of the complexing ligand content. As soon as thecomplexing ligand has completely reacted to give the correspondingoxide, the oxidation reaction is ended.

[0044] In a proven embodiment, a suitable reactor, for example, astirred reactor equipped with an inlet nozzle and frit attachment or atubular reactor provided with a gas distributor plate, which may containa random packing, is charged with the organic phase and the oxygen oroxygen-containing gas mixture is passed upward through the organicphase.

[0045] The organic phase obtained after the oxidative treatment is thenextracted with an aqueous solution of a water-soluble complexing ligand.The water-soluble complexing ligands are generally phosphines of theformula

[0046] Ar¹, Ar² and Ar³ are each a phenyl or naphthyl group, Y¹, Y² andY³ are each a straight-chain or branched alkyl group having from 1 to 4carbon atoms, an alkoxy group, a halogen atom, an OH, CN, NO₂ or R⁷R⁸Ngroup, where R⁷ and R⁸ are each a straight-chain or branched alkyl grouphaving from 1 to 4 carbon atoms, X¹, X² and X³ are each a carboxylate(COO⁻) and/or sulfonate (SO₃ ⁻) radical, n₁, n₂ and n₃ are identical ordifferent numbers from 0 to 5, M is an alkali metal ion, the equivalentquantity of an alkaline earth metal or zinc ion or an ammonium orquaternary alkylammonium ion of the formula N(R⁹R¹⁰R¹¹R¹²)⁺, where R⁹,R¹⁰, R¹¹ and R¹² are each a straight-chain or branched alkyl grouphaving from 1 to 4 carbon atoms, and m₁, m₂ and m₃ are identical ordifferent integers from 0 to 3, and at least one number m₁, m₂ or m₃ isequal to or greater than 1.

[0047] The aqueous solution contains from 1 to 40, in particular from 10to 20, preferably from 10 to 15% by weight of water-soluble complexingligands, based on the aqueous solution.

[0048] The aqueous solution comprising the complexing ligands is used insuch a quantity that the molar ratio of rhodium to phosporus III is from1:1 to 1:200, preferably 1:10 to 1:20. The concentration ofwater-soluble ligands in the aqueous solution is chosen taking intoaccount the desired molar ratio of rhodium to phosphorus III and againstthe background that the organic and aqueous phases should be present ina quantity ratio suitable for phase separation. In general, the volumeratio of organic to aqueous phase is from 30:70 to 70:30.

[0049] The extraction of the rhodium from the organic into the aqueousphase is carried out at elevated pressure and elevated temperature. Ingeneral, pressures of from 1 to 20 MPa, preferably from 1 to 10 MPa, inparticular from 2.5 to 5 MPa and at temperatures of from 20 to 200° C.,preferably from 50 to 150° C., in particular from 120 to 140° C. areemployed.

[0050] The extraction is carried out either under the autogenouspressure, under pressurization of an inert gas, for example, nitrogen ora noble gas, or under synthesis gas pressure. The extraction time isgenerally from 0.5 to 5 hours.

[0051] It is particularly advantageous to carry out the extraction inthe presence of synthesis gas. The composition of the synthesis gas,i.e. the ratio of hydrogen to carbon monoxide, may vary within a widerange. In general, the molar ratio of hydrogen to carbon monoxide isfrom 1:10 to 10:1. Mixtures which comprise hydrogen and carbon monoxidein a molar ratio of 1:1 are particularly suitable.

[0052] The extraction with aqueous complexing ligand solution undersynthesis gas conditions leads to water-soluble rhodium complexes which,as well as the complexing ligands, also contain carbon monoxide andhydrogen in complexed form. Catalytic activity is ascribed to suchrhodium complexes and the aqueous catalyst solution obtained after phaseseparation may be used without further treatment for hydroformylatingolefins by the biphasic process, as disclosed, for example, by DE-C-2627 354.

[0053] However, it is also possible to subject the aqueousrhodium-containing solution obtained by the process according to theinvention to a further oxidation after adding a water-soluble salt of acarboxylic acid having from 7 to 22 carbon atoms in excess, based onrhodium, a process disclosed, for example, by EP-B1-0 255 673 andEP-B1-0 367 957. Rhodium can be precipitated from this aqueous solutionas a sparingly water-soluble or insoluble compound, for example, in theform of rhodium 2-ethylhexanonate, and be used in a hydroformylationprocess carried out monophasically in the organic phase. Such ahydroformylation process is disclosed, for example, by EP-B1-0 188 246.

[0054] As disclosed by EP-B1-0 255 673, useful oxidizing agents arepreferably oxygen or oxygen-containing gas mixtures, for example air.However, it is also possible to use other oxidizing agents, such ashydrogen peroxide, hydrogen peroxide-forming compounds, hypochlorite,chromates or permanganates. The oxidative treatment leads todecomposition of the rhodium complex containing the water-solubleligands by the formation of phosphorus (V) oxide compounds which are nolonger capable of forming complexes from the water-soluble phosphinesused in the extraction step. During the oxidation procedure, rhodiumprecipitates in the form of water-insoluble compounds, presumably asrhodium carboxylate. The oxidation is carried out at a temperature offrom 50 to 200° C. at atmospheric pressure or at elevated pressure offrom 0.1 to 2.0 MPa over a period of from 0.5 to 24 hours. In anextension of the teaching of EP-B1-0 255 673 and EP-B1-0 367 957, theaqueous solution is extracted after the oxidation step using an organicsolvent comprising an organic phosphine or diphosphine. The organicsolvent used is an aliphatic hydrocarbon having from 6 to 12 carbonatoms, an aromatic hydrocarbon having from 6 to 12 carbon atoms,preferably benzene, toluene or the isomeric xylenes, ethers, forexample, diethyl ether, dibutyl ether, or alcohols, for example,butanol, the isomeric pentanols, ethylene glycol or diethylene glycol.The phosphines or diphosphines used may be, for example,triphenylphosphine, tributylphosphine, tripropylphosphine,triethylphosphine, trioctylphosphine, diethylphenyl-phosphine,diphenylethylphosphine, diphenyl-(dimethylamino)phenyl-phosphine,methylcyclohexylanisylphosphine,2,2′-bis((diphenylphosphino)methyl)-1,1′-biphenyl,1,2-bis(diphenylphosphino)ethane or2,2′-bis((diphenylphosphino)methyl)-1,1′-binaphthyl.

[0055] The extraction of this solution using phosphines or diphosphinesdissolved in an organic solvent allows rhodium to be transferredvirtually quantitatively from the aqueous into the organic phase.

[0056] The extraction of the rhodium from the aqueous into the organicphase is carried out under elevated pressure and elevated temperature.In general, pressures of from 1 MPa to 20 MPa, preferably from 1 MPa to10 MPa, in particular from 2.5 MPa to 5 MPa and temperatures of from 20°C. to 200° C., preferably from 50° C. to 150° C., in particular from120° C. to 140° C. are employed.

[0057] The extraction is carried out either under autogenous pressure,under pressurization of an inert gas, for example, nitrogen or a noblegas, or under synthesis gas pressure. The extraction time is generallyfrom 0.5 to 5 hours.

[0058] It is particularly advantageous to carry out the extraction inthe presence of synthesis gas. The composition of the synthesis gas,i.e. the ratio of hydrogen to carbon monoxide, may vary within a widerange. In general, the molar ratio of hydrogen to carbon monoxide isfrom 1:10 to 10:1. Mixtures which comprise hydrogen and carbon monoxidein a molar ratio of 1:1 are particularly suitable.

[0059] The organic solution comprising the complexing ligands is used insuch a quantity that the molar ratio of rhodium to phosporus III is from1:1 to 1:200, preferably 1:10 to 1:20. The concentration of ligands inthe organic solution is chosen taking into account the desired molarratio of rhodium to phosphorus III and against the background that theorganic and aqueous phases should be present in a quantity ratiosuitable for phase separation. In general, the volume ratio of organicto aqueous phase is from 30:70 to 70:30.

[0060] The rhodium-containing organic solution obtained by this methodcan be used as the catalyst solution in the hydroformylation processcarried out homogeneously, as disclosed, for example, by EP-B1-0 188246.

[0061] The process according to the invention can be used with greatsuccess to remove and recover rhodium from the products ofhydroformylation of terminal and internal olefins having more than 3carbon atoms. When branched olefin starting materials are used, theprocess according to the invention is particularly suitable for removingrhodium from the reaction products which [lacuna] from thehydroformylation of i-heptene, diisobutylene, tri- and tetrapropylene orof C8-olefins commercially available under the description Dimersol.When unbranched olefins are used in the hydroformylation reaction, thework up process according to the invention can be used with particularsuccess with hydroformylation products of propylene, n-butene, n-penteneand n-hexene, although the absolute rhodium concentrations are generallylower.

[0062] The process according to the invention can be used with greatsuccess when hydroformylation steps hitherto carried out under cobaltcatalysis are converted to the rhodium method, a process disclosed byEP-0 805 138, which is a further development of the process according toEP-0 111 257.

[0063] The process according to the invention may enable more than 95%of the rhodium originally present to be recovered. The cobalt content inthe concentrated rhodium solution obtained is less than 1%, based on thesum of the metals rhodium and cobalt.

[0064] It will be appreciated that the process according to theinvention is not restricted to the work up of solutions which, as wellas rhodium, also contain cobalt compounds as impurities. It can also beused with catalyst solutions which stem from a process carried out underexclusive rhodium catalysis. The nonlimiting examples which followillustrate the invention.

1^(st) EXAMPLE Work Up of a Used Rhodium/triphenylphosphine-containingSolution

[0065] 1 000 g of a used catalyst solution having the followingcomposition: 55% by weight of n-butyraldehyde, 2% by weight oftriphenylphosphine oxide, 6.3% by weight of triphenylphosphine, 36.2% byweight of high-boilers (generally aldol condensation products ofbutyraldehyde) and 0.5% by weight of low-boilers (generally hydrocarbonshaving from 3 to 7 carbon atoms) and comprising 699 mg of rhodium (6.79mmol) and 234 mg of cobalt (3.97 mmol) are diluted by mixing with 1 000g of fresh n-butyraldehyde in a 4 l three-necked flask and thenextracted twice with 100 g of 65% phosphoric acid for 30 minutes at 22°C. each time. The phases are separated under gentle stirring likewisewithin 30 minutes. The organic phase is then washed twice with 50 g ofdeionized water each time which had been set using 3 ml of NaOH (10%strength) to a pH of 5.8. After subsequent phase separation, theremaining organic phase is transferred to a 4 l three-necked flaskequipped with a frit attachment and frit filter and aerated with 150 l/hof air at 55° C. over 12 hours at 55° C. After the oxidation had ended,1969 g of organic phase were obtained. The organic phase is transferredtogether with 199.8 g of an aqueous solution of trisodiumtri(m-sulfophenyl)phospine (TPPTS) (corresponds to 101.9 mmol of P III,Rh: P=1:15) into a 5 l steel autoclave and stirred in intensively for 3hours at 5 MPa of CO/H₂ pressure at 125° C. The reaction mixture is thentransferred to a 4 l three-necked flask equipped with a lower outlet andlower aqueous phase (144.2 g) is removed from the upper organic phase(1979 g). The aqueous TPPTS solution contains 687.7 mg of rhodium,corresponding to 98.4% of the rhodium quantity originally present in thestarting solution. The cobalt content in the aqueous TPPTS solution wasbelow the analytical detection limit.

2^(nd) EXAMPLE Hydroformylation of Propylene Using the Rh/TPPTS SolutionObtained in Example 1

[0066] The Rh/TPPTS solution (P:Rh=14:1) obtained according to example 1is adjusted by adding fresh TPPTS to a P:Rh ratio of 100:1. The rhodiumcontent is 260 ppm. The solution is charged into a 0.2 l stainless steelautoclave. The 0.2 l stainless steel autoclave equipped with a stirreris charged with propylene and a CO/H₂ mixture consisting of equal volumefractions in such a quantity as 10 l/h (STP) of off gas may be withdrawnfrom the reactor [l/h (STP) means 1 liter of off gas under atmosphericconditions (20° C. and 1 at) per hour]. At the same time, 300 ml perhour of aqueous catalyst solution are circulated through the reactor.The hydroformylation is carried out semicontinuously over 8 hours. Theremaining reaction parameters and the results of the hydroformylationare given in table 1. TABLE 1 Hydroformylation of propylene in thepresence of a worked-up catalyst solution Experiment duration [h] 8Temperature [° C.] 122 Pressure [bar] 50 Rh content [mg/kg] 260 P (III)content [mmol/kg] 263 Ligand/Rh 100 C3 introduction rate [g/h] 40Activity [mol of aldehyde/mol of Rh · min] 15.08 Productivity [kg ofaldehyde/l cat. sol. · h] 0.213 Conversion [%] 37 n/i ratio 93/7

3^(rd) EXAMPLE Comparative Hydroformylation Example

[0067] A freshly prepared TPPTS solution is installed with 260 ppm ofrhodium acetate in the 0.2 l stainless steel autoclave. The P:Rh ratiois 100:1. Otherwise, the hydroformylation reaction is carried out as inexample 2. The remaining reaction parameters and the results of thehydroformylation are given in table 2. TABLE 2 Hydroformylation ofpropylene in the presence of a fresh catalyst solution Experimentduration [h] 8 Temperature [° C.] 122 Pressure [bar] 50 Rh content[mg/kg] 260 P (III) content [mmol/kg] 265 Ligand/Rh 100 C3 introductionrate [g/h] 40 Activity [mol of aldehyde/mol of Rh · min] 15.53Productivity [kg of aldehyde/I cat. sol. · h] 0.216 Conversion [%] 38n/i ratio 93/7

[0068] As comparison of tables 1 and 2 shows, the work up processaccording to the invention delivers a catalyst solution (table 1) whichhas virtually the same activity, productivity and conversion numbers asa freshly prepared catalyst solution using a fresh rhodium quantity(table 2).

1. A process for recovering rhodium from organic solutions comprisingrhodium complexes with or without cobalt complexes and with or withoutcomplexing ligands, which comprises extracting the organic phase with anaqueous solution of a phosphate of the formula (O)P(OR¹)(OR²)(OR³),where R¹, R² and R³ are identical or different and are hydrogen, astraight-chain or branched alkyl radical having 1-10 carbon atoms or asubstituted or unsubstituted aryl radical having 6-10 carbon atoms, andthe aryl radical is substituted by straight-chain or branched alkylradicals having 1-4 carbon atoms, or with a phosphonate of the formulaR⁴P(O)(OR⁵)(OR⁶), where R⁴, R⁵ and R⁶ are identical or different and arehydrogen, a straight-chain or branched alkyl radical having 1-10 carbonatoms or a substituted or unsubstituted aryl radical having 6-10 carbonatoms, and the aryl radical is substituted by straight-chain or branchedalkyl radicals having 1-4 carbon atoms; washing the organic phase withwater at a pH of from 0 to 8; treating the organic phase after phaseseparation with an oxidizing agent at a temperature of from 0 to 100°C.; treating the organic phase with an aqueous solution of awater-soluble arylphosphine at elevated temperature and elevatedpressure; and removing the rhodium-containing aqueous solution from theorganic phase by phase separation.
 2. The process as claimed in claim 1,wherein the organic phase is extracted with the aqueous solution of thephospate or phosphonate as defined in claim 1 at atmospheric pressure ata temperature of from 0 to 100° C., preferably from 20 to 40° C.
 3. Theprocess as claimed in claim 1, wherein the organic phase is extractedwith the aqueous solution of the phosphate or phosphonate as defined inclaim 1 at a pressure of from 0.5 to 20 MPa and at a temperature of from100 to 200° C., preferably from 120 to 140° C.
 4. The process as claimedin one of claims 1-3, wherein R¹, R², R³, R⁴, R⁵ and R⁶ are identical ordifferent and are a straight-chain or branched alkyl radical having from1 to 5 carbon atoms.
 5. The process as claimed in one of claims 1 to 4,wherein a phosphoric acid, trimethyl phosphate or methyldimethylphosphonate extractant is used.
 6. The process as claimed in oneof claims 1 to 5, wherein the water wash is effected at a pH of from 4to
 8. 7. The process as claimed in one of claims 1 to 6, wherein theorganic phase is oxidized using oxygen, oxygen-containing gas mixtures,hydrogen peroxide, hydrogen peroxide-forming compounds, hypochlorite,chromates or permanganates.
 8. The process as claimed in claim 7,wherein the oxidizing agent used is air.
 9. The process as claimed inone of claims 1 to 8, wherein the oxidation is carried out at atemperature of from 30 to 60° C., preferably from 50 to 60° C.
 10. Theprocess as claimed in one of claims 1 to 9, wherein the oxidation iscarried out at a pressure of from 0.1 to 2.0 MPa, preferably from 0.2 to1 MPa and in particular from 0.3 to 0.7 MPa.
 11. The process as claimedin one of claims 1 to 10, wherein the organic phase obtained afteroxidative treatment is extracted with an aqueous solution of a phospineof the formula

where Ar¹, Ar² and Ar³ are each a phenyl or naphthyl group, Y¹, Y² andY³ are each a straight-chain or branched alkyl group having from 1 to 4carbon atoms, an alkoxy group, a halogen atom, an OH, CN, NO₂ or R⁷R⁸Ngroup, where R⁷ and R⁸ are each a straight-chain or branched alkyl grouphaving from 1 to 4 carbon atoms, X¹, X² and X³ are each a carboxylate(COO⁻) and/or sulfonate (SO₃ ⁻) radical, n₁, n₂ and n₃ are identical ordifferent numbers from 0 to 5, M is an alkali metal ion, the equivalentquantity of an alkaline earth metal or zinc ion or an ammonium orquaternary alkylammonium ion of the formula N(R⁹R¹⁰R¹¹R¹²)⁺, where R⁹,R¹⁰, R¹¹ and R¹² are each a straight-chain or branched alkyl grouphaving from 1 to 4 carbon atoms, and m₁, m₂ and m₃ are identical ordifferent integers from 0 to 3, and at least one number m₁, m₂ or m₃ isequal to or greater than
 1. 12. The process as claimed in claim 11,wherein the extraction is carried out at pressures of from 1 to 20 MPa,preferably from 1 to 10 MPa, in particular from 2.5 to 5 MPa and attemperatures of from 20 to 200° C., preferably from 50 to 150° C. and inparticular from 120 to 140° C.
 13. The process as claimed in one ofclaims 10 to 12, wherein the extraction is carried out in the presenceof synthesis gas.
 14. A catalyst for hydroformylating aldehydescomprising rhodium obtainable according to one of claims 1 to 13 for abiphasic hydroformylation process carried out in the presence of water.15. The use of the aqueous rhodium-containing solution obtainableaccording to one of claims 1 to 13 as the catalyst solution for ahydroformylation process carried out in the presence of water.
 16. Aprocess for recovering rhodium from organic solutions comprising rhodiumcomplexes with or without cobalt complexes and with or withoutcomplexing ligands, which comprises treating the aqueousrhodium-containing solution obtainable according to claims 1 to 13 at atemperature of from 50 to 200° C. and a pressure of from 0.1 to 2.0 MPawith an oxidizing agent and then extracting with an organic solventcomprising an organic phosphine or diphosphine.
 17. The process asclaimed in claim 16, wherein the oxidizing agent used is oxygen,oxygen-containing gas mixtures, air, hydrogen peroxide, hydrogenperoxide-forming substances, hypochlorite, chromates or permanganates.18. The process as claimed in one of claims 16 or 17, wherein theorganic phosphine or diphosphine used is triphenylphosphine,tributylphosphine, tripropylphosphine, triethylphosphine,trioctylphosphine, diethylphenylphosphine, diphenylethylphosphine,diphenyl-(dimethylamino)phenylphosphine,methylcyclohexylanisyl-phosphine,2,2′-bis((diphenylphosphino)methyl)-1,1′-biphenyl,1,2-bis(diphenylphosphino)ethane or2,2′-bis((diphenylphosphino)-methyl-1,1′-binaphthyl.
 19. The process asclaimed in one of claims 16 to 18, wherein the extractant used is analiphatic hydrocarbon having from 6 to 12 carbon atoms, an aromatichydrocarbon having from 6 to 12 carbon atoms, an ether or an alcohol.20. The process as claimed in claim 19, wherein the extractant used isbenzene, toluene, the isomeric xylenes, diethyl ether, dibutyl ether,butanol, the isomeric pentanols, ethylene glycol or diethylene glycol.21. The process as claimed in one of claims 16 to 20, wherein theextraction is carried out at pressures of from 1 to 20 MPa, preferablyfrom 1 to 10 MPa and in particular from 2.5 to 5 MPa and at temperaturesof from 20 to 200° C., preferably from 50 to 150° C. and in particularfrom 120 to 140° C.
 22. The process as claimed in one of claims 16 to21, wherein the extraction is carried out in the presence of synthesisgas.
 23. A catalyst for hydroformylating aldehydes comprising rhodiumobtainable according to one of claims 16 to 22 for a monophasichydroformylation process carried out in an organic phase.
 24. The use ofthe organic rhodium-containing solution obtainable according to one ofclaims 16 to 22 as the catalyst solution for a hydroformylation processcarried out in an organic phase.